Recently, distributing wires or interconnections of, for instance, copper (Cu) or aluminum (Al) have been adopted in the field of LSI and simultaneously, there have widely been conducted researches in and development of the interconnection structure and interlayer insulating films. However, it is difficult to effectively reduce the interconnecting delay by simply using the interconnection of, for instance, Cu. For this reason, in the semiconductor device-fabricating process, an oxide film (such as a SiO2 film) having a low relative dielectric constant is used as an interlayer insulating film and there has been proposed such an idea that the oxide film is converted into or replaced with a porous oxide film from the viewpoint of further reduction of the relative dielectric constant of such an oxide film. For instance, there has been proposed a technique for forming a porous SiO2 film having a lower relative dielectric constant through the silylation of an inorganic SOG (spin on glass), while making use of the conventional SOG coating technique. In addition, it has also been proposed to form a SiO2 film having a low relative dielectric constant by the plasma polymerization of an organic silane according to the plasma CVD technique.
If a SiO2 film is formed according to the conventional technique and then a film is further deposited on the SiO2 film in the semiconductor device-fabricating process such as the CVD process, a problem arises, such that the relative dielectric constant of the resulting product increases. In the case of the porous SiO2 film formed using an inorganic SOG, a problem arises such that the diameter of the holes present in the resulting porous film is too large to reduce the relative dielectric constant thereof by the formation of fine pores. In addition, in the case of the SiO2 film formed using an organic silane, problems arise such that the resulting film is insufficient in the film quality and that the heat-resistant temperature thereof is low (not more than 450° C.).
Therefore, the first object of the present invention is to eliminate the foregoing drawbacks associated with the conventional techniques and more specifically to provide a method for preparing a porous SOG film or an interlayer insulating film (or interlayer dielectric) having a low relative dielectric constant, whose dielectric constant is never changed even when a film is further deposited on the SOG film according to, for instance, the CVD process after the formation of this interlayer insulating film (first invention).
Moreover, it has been known that the porous film formed by the foregoing conventional method absorbs moisture since the film has hygroscopicity due to the porous characteristics thereof and this in turn leads to corrosion of interconnections of, for instance, Al. For this reason, there have been proposed methods of chemical treatments for making the inner surface of the holes in the film hydrophobic by replacing the hydrophilic OH groups remaining on the porous film with hydrophobic CH3 groups or by subjecting the OH groups to dehydration to thus convert them into SiO2, for the improvement of the hygroscopicity of the film.
Moreover, even in the method for preparing a porous SOG film (or an interlayer insulating film) having a low relative dielectric constant, whose dielectric constant never causes any change when depositing another film on the interlayer insulating film according to, for instance, the CVD process after the formation of the interlayer insulating film, the penetration of moisture such as water vapor through the surface of the resulting porous SiO2 film often becomes a cause of a critical problem, since the holes present therein are arranged perpendicularly to the substrate. Further, the inorganic SOG film includes a large quantity of OH groups and therefore, unreacted OH groups may still remain in the film even after the firing of the same. Accordingly, a problem arises such that the moisture in the atmosphere is adsorbed on the film through the residual OH groups and this results in the corrosion of the Al interconnections. Moreover, the foregoing chemical processing suffers from a problem of the difficulty in the control of the process.
Accordingly, it is the second object of the present invention to solve the foregoing problems of the moisture (such as water vapor)-penetration through the film surface and the hygroscopicity thereof and more specifically to provide a method for preparing a multi-layered porous SOG film or a mono-layered porous SOG film or an interlayer insulating film having a low relative dielectric constant, which can inhibit any moisture-penetration through the film surface and reduce the hygroscopicity of the film and whose dielectric constant never cause any change even when an additional film is deposited on the insulating layer according to, for instance, the CVD process after the formation of the insulating film (second invention).
It is the third object of the present invention to solve the foregoing problem caused by the presence of unreacted OH groups in a porous SOG film by the removal of the OH groups from the porous film and more specifically to provide a method for preparing a porous SOG film or an interlayer insulating film having a low relative dielectric constant, which is not changed at all even when an additional film is deposited on the insulating layer according to, for instance, the CVD process after the formation of the insulating film (third invention).
Moreover, it is the fourth object of the present invention to solve the foregoing problem caused by the presence of unreacted OH groups in a porous SOG film and more specifically to provide a method for preparing a porous SOG film or a porous interlayer insulating film, which does not have any OH group at least on the inner wall of the holes and thus has a low relative dielectric constant, whose dielectric constant is never changed even when an additional film is deposited on the insulating layer according to, for instance, the CVD process after the formation of the insulating film, the method being characterized in that the process control thereof is very easy (fourth invention).